[glyf] remove_hinting should del program from composite glyph

Unlike simple glyphs, which always have 'program' attribute (even when empty, with no instructions)
in composite glyphs, it's the presence of 'program' attribute that determines whether
the optional WE_HAVE_INSTRUCTIONS component flag is set or not.
Thus, the trim method (with remove_hinting=True) should delete the attribute for
composite glyphs.

Fixes https://github.com/fonttools/fonttools/issues/1550

Lib/fontTools/ttLib/tables/_g_l_y_f.py

@@ -917,8 +917,12 @@ class Glyph(object):
 			expanding it."""
 		if not hasattr(self, "data"):
 			if remove_hinting:
-				self.program = ttProgram.Program()
-				self.program.fromBytecode([])
+				if self.isComposite():
+					if hasattr(self, "program"):
+						del self.program
+				else:
+					self.program = ttProgram.Program()
+					self.program.fromBytecode([])
 			# No padding to trim.
 			return
 		if not self.data:

Tests/ttLib/tables/_g_l_y_f_test.py

@@ -4,6 +4,7 @@ from fontTools.misc.fixedTools import otRound
 from fontTools.pens.ttGlyphPen import TTGlyphPen
 from fontTools.ttLib import TTFont, newTable, TTLibError
 from fontTools.ttLib.tables._g_l_y_f import GlyphCoordinates
+from fontTools.ttLib.tables import ttProgram
 import sys
 import array
 import pytest
@@ -240,6 +241,41 @@ class glyfTableTest(unittest.TestCase):
         with self.assertRaisesRegex(TTLibError, "glyph '.' contains a recursive component reference"):
             glyph_A.getCoordinates(glyphSet)
 
+    def test_trim_remove_hinting_composite_glyph(self):
+        glyphSet = {"dummy": TTGlyphPen(None).glyph()}
+
+        pen = TTGlyphPen(glyphSet)
+        pen.addComponent("dummy", (1, 0, 0, 1, 0, 0))
+        composite = pen.glyph()
+        p = ttProgram.Program()
+        p.fromAssembly(['SVTCA[0]'])
+        composite.program = p
+        glyphSet["composite"] = composite
+
+        glyfTable = newTable("glyf")
+        glyfTable.glyphs = glyphSet
+        glyfTable.glyphOrder = sorted(glyphSet)
+
+        composite.compact(glyfTable)
+
+        self.assertTrue(hasattr(composite, "data"))
+
+        # remove hinting from the compacted composite glyph, without expanding it
+        composite.trim(remove_hinting=True)
+
+        # check that, after expanding the glyph, we have no instructions
+        composite.expand(glyfTable)
+        self.assertFalse(hasattr(composite, "program"))
+
+        # now remove hinting from expanded composite glyph
+        composite.program = p
+        composite.trim(remove_hinting=True)
+
+        # check we have no instructions
+        self.assertFalse(hasattr(composite, "program"))
+
+        composite.compact(glyfTable)
+
 
 if __name__ == "__main__":
     import sys